Apparatus for automatic pitch compensation in marine vessels

ABSTRACT

Pneumatic control circuit for marine vessel having controllable pitch propeller. Manual pneumatic signals of pitch and throttle are modified by automatic pitch compensator coupled to engine governor output, which senses changes in governor throttle demand, changes being a measure of change in engine load condition. Particular embodiments of automatic pitch compensators can be coupled to governor having output shaft of relatively high torque, or relatively low torque, or governor with hydraulic pressure ports.

United States Patent 1 Kobelt Jack R.'Kobelt, 6110 Oak Street, Vancouver 13, British Columbia, Canada Feb. 23, 1971 [76] Inventor:

[22] Filed:

211 Appl. No.: 117,962

[52] us. Cl. ..4l6/27 [51] vInt. Cl. ..B63h 3/10 [58] Field of Search 416/25, 27

[56] References Cited UNITED STATES PATENTS 2,878,880 3/1959 Gillespie ..416/27 2,958,381 11/1960 Stevens et ....416/27 3,088,523 5/1963 Smalley et al. ..416/27 X sac ' 1 51 Apr. 3, 1973 3,110,348 11/1963 Greiner 416/27 7 3,302,724 2/1967 Brooks et al. ..4 16/27 3,588,272 6/1971 Kristinehamn et al .14 1 6/27 X Primary Examiner-Everette A. Powell, Jr. Attorney-Brian J. Wood 57 7 ABSTRACT Pneumatic control circuit'for marine vessel having controllable pitch propeller. Manual pneumatic signals of pitch and throttle are modified by automatic pitch compensator coupled to engine governor output, which senses changes in governor throttle demand, changes being a measure of change in engine load condition. Particular embodiments of automatic pitch compensators can be coupled to governor having output shaft of relatively high torque, or relatively low torque, or governor with hydraulic pressure ports,

11 Claims, 9 Drawing Figures PATENTEDAPRS I975 3.724.970

Jack R. Kobe 1t In or Lyle G Tropey,

A ent PATENTEDAPR3 I975 3.724.970

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I 1 II Jack R. Kobelt Inve tor PATENTEDAFR 3 I975 SHEET t UP 4 Inventor Jack R. Kobelt b y X7 Ly 1e Ttorey,

Agent BACKGROUND OF THE INVENTION 1. FIELD OF THE INVENTION The invention relates to a pneumatic circuit and components for use in power control installations in marine vessels, particularly tugs, in which a single lever, or equivalent two lever, control concurrently controls throttle, and pitch of a controllable pitch propeller.

2. PRIOR ART Commonly, pneumatic control installations using a single lever control have a programmed sequence of increase of throttle setting. Conditions arise when, for a given pitch setting, the vessel does not attain sufflcient speed to permit the engine to operate at the pro-.

grammed rpm at the programmed pitch. Consequently the engine becomes overloaded in these conditions.

Load on the engine varies from a first condition when the tug is travelling at full speed without a barge, to a second condition when the tug is towing a maximum displacement barge. A third condition alternating between extremes of the first and second conditions occurs in heavy sea when with a long period of swell e.g. over thirty seconds between wave crests, wave motion causes relative movement between the tug and the barge slackening thetow line and producing fluctuations in engine load. The two extreme conditions require different pitch settings of the propeller, and compensation for the fluctuations in load without manual adjustment of the single lever control is desireable. Manual override systems are known, but require surveillence and, as such, are subject to human error with a risk of damage to the engine.

SUMMARY OF THE INVENTION rotation of a governor output shaft; or hydraulic by way of hydraulic pressure outputs from an engine governor. Air from a supply source is fed into the pitch compensator and is metered to pilot pressure, which pressure reflects an amount of pitch compensation required to maintain the engine at a pre-set rpm. The operative connection between the automatic pitch compensator and the engine rpm control device is selected to be compatible with characteristics of both.

The first embodiment of an automatic pitch compensator has a connection to the air metering means in- Hydraulic circuit and components according to the compensator'according to the invention, the compensator being linked to a fuel rack of the engine or other rpm control device. A change in fuel rack position is detected by the compensator, such change resulting from a demand from the governor fora change in fuel delivery to the engine which, without such change in fuel would change speed from that initially set by a throttle control.

A forward pitch pneumatic line from the single lever control is in circuit with a compensating relay valve operated by pilot pressure from the automatic pitch compensator.

Three embodiments of the automatic pitch compensator are described. Each embodiment includes an air metering means incorporated in a compensating air pressure regulating valve, operativelyconnected to an engine rpm control device. Such connection is mechanical by way of a fuel rack of an engine, or by cluding a lever pivoted at a fulcrum, adjacent a pushrod end of the regulating valve, an opposite end of the lever being mechanically linked to the fuel rack of the engine or an output shaft of the governor.

The second embodiment of the automatic pitch compensator has a servo device in which engine oil flowing through the automatic pitch compensator is metered by relative positions of a plug and metering bore within a piston actuating rod, relative positions of both reflecting amount of pitch compensation required to maintain engine at selected rpm and being controlled by position of the fuel rack or governor output shaft. The piston rod has a cam, position of which cam determines degree of metering in the regulating valve. This type of compensator is selected forum with governors with inadequate torque at the output shaft to actuate the regulating valve directly.

A third type of automatic pitch compensator is selected for use with governors having hydraulic outputs and is connected to hydraulic pressure ports of the governor. Fluid volume flow and direction between the ports reflects anamount of pitch compensation and I to maintain the predetermined rpm. The signal also changes pilot pressure output from the regulating valve of the compensator. Pilot pressure change modifies output of the compensating relay valve in such a manner that the signal to the pitch control cylinder for forward pitch as determined by the manual control is compensated to suit current engine loading conditions. Thus, the propeller operates at a compensated pitch, which pitch 'without the pitch compensator would cause undesirable engine operation. Fuel delivery to the engine is also changed by the compensation, thus by successive approximation, the pitch is matched to engine load.

A detailed description following, related to drawings, gives exemplification of apparatus and method according to the invention which, however, is capable of expression in method and means other than particularly described and illustrated.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic of a hydraulic circuit associated with an automatic pitch compensator, single lever control, and related components,

FIG. 2 is a fragmented side elevation of a mechanically actuated automatic pitch compensator,

FIG. 3 is a fragmented end elevation seen from 33 of FIG. 2,

FIG. 4 is a partially sectioned side elevation of a hydraulic servo actuated automatic pitch compensator, FIG. 5 is a top plan view seen from 55 of FIG. 4,

FIG. 6 is a partially sectioned side elevation of a hydraulically actuated automatic pitch compensator,

FIG. 7 is a top plan view seen from 77 of FIG. 6,

FIG. 8 is a section of a biased flow control needle valve means used in the embodiment shown in FIGS. 6 and 7,

FIG. 9 shows the schematic circuit of FIG. 1 with diagrammatic representations of operative connection of components to a variable pitch propeller and to a governor of an engine.

Left hand and right hand designations apply to the automatic pitch compensators as shown in FIGS. 4 and 6.

DETAILED DISCLOSURE FIGS. 1 and 9, circuit and components A circuit 10, shown schematically, is a means of compensating a manually selected signal for forward pitch of a controllable pitch propeller, 253 FIG. 9 only. Compensation of pitch is required because of changes of load imposed on the engine. The compensation alters fuel delivery to an engine 252, FIG. 9 only, to maintain a predetermined rpm. A signal from a governor 251, FIG. 9 only, to change the fuel delivery from that originally delivered by a throttle control is used as a measure of engine load.

A single lever control box 11, hereinafter SLC 11, operated by a hand lever 12, has three cam operated pneumatic metering valves 13, 14, 15, the valve 13 controlling reverse pitch of the propeller, the valve 14 forward pitch, and the valve 15 throttle control. With a single lever control, movement of the lever controls pitch and throttle concurrently. A two lever control (not shown) can be substituted for the single lever control in which case the pitch and throttle signals are independent. Single lever and two lever controls as above are herein referred to generically as manual pitch and throttle controls. With either type of control box, movement of a lever or levers adjusts pitch of the propeller and the valve 15, which valve is used to set input to the governor 251, controls the rpm at which the engine is to operate. In usual engine/governor setups, the governor attempts to maintain the engine at the pre-set rpm by changes in the fuel supply. This can result in overload.

Filtered, compressed, and dried air from a source 254, (FIG. 9 only), entering the valves through an inlet line 17 is directed and metered by means of the lever 12 and the valves to a pneumatic line associated with the control mechanism. To ensure reliable operation under severe conditions likely to be encountered in marine installations, dry filtered air is specified. Hereinafter and in the claims, air under pressure means dry filtered air as above.

The valve 13 has an outlet pneumatic line 16 leading to a reverse pitch port 18 of a pitch control cylinder 19, hereinafter PCC 19. The PCC 19 controls a known pitch changing mechanism of a hub of the controllable pitch propeller 253, and is also known as a positioner cylinder. The PCC 19 is linked mechanically, as seen at 255 FIG. 9 only, to the pitch changing mechanism and effectively controls a hydraulic servo valve, which in turn controls hydraulic pressure to the pitch changing mechanism. The PCC and means of linking to the controllable pitch propeller are well known.

The valve 14 has an outlet pneumatic line 21 leading to an inlet port 22 of a compensating relay valve 23, hereinafter CRV 23. An outlet port 24 communicates with a forward pitch port 26 of the PCC 19. Pressure in the pneumatic line 25 is modified from the pressure in the line 21 through a metering means within the CRV 23, metering being controlled by pilot pressure within a pneumatic line 27 which enters the valve 23 at a pilot pressure input port 29. The CRV 23 is of a known type such that, for a given input pressure at the port 22, an increase in pilot pressure at the port 29 proportionally increase output pressure at the port 24. Thus output pressure in the line 25 is regulated by an automatic pitch compensator as is later explained. An accumulator tank 31 is provided in the line 27, the tank serves as a buffer means against sudden pressure changes which occur when adjusting response of the circuit in initial setting up, by providing a relatively large volume of air to decrease sensitivity of needle valve adjustments when setting response of the circuit.

A pneumatic line 32 connects the accumulator tank 31 with a pilot pressure outlet port 34 of an automatic pitch compensator 36 according to the invention, hereinafter AFC 36.

Three embodiments of the APC are described all serve essentially the same purpose, namely being means to effect automatic pneumatic modification of manually selected pitch signals to the PCC 19, i.e. of the selected pitch output of the SLC.

A pneumatic line 37 transmits air from the line 17 to an inlet port 38 of the AFC 36. The AFC 36 has an exhaust port 39 vented to atmosphere. An engine rpm control device, suitably a fuel rack (not shown) of an engine or a governor output shaft, 251.1, FIG. 9, is connected to a coupling means 41 of the APC, so that the APC senses a demand to the engine to change fuel delivery. The throttle control valve 15 is connected through a pneumatic line 42 to an inlet port 43 of a throttle control 44, hereinafter TC 44.

The circuit 10 does not provide automatic pitch compensation for reverse pitch. In the neutral pitch position the lever 12 does not actuate the valves 13 or 14 and pressure in the lines 21 and 16 is low and essentially constant. To attain forward pitch from neutral, the valve 14 is actuated and meters air into the forward pitch line 21, pressure in the reverse pitch line 16 being unchanged. If forward pitch is reduced towards neutral, but not passing into reverse pitch, pressure in the line 21 is reduced and pressure in the line 16 still remains unchanged. The PCC 19 has a neutral position, i.e. neutral pitch, which is attained when there is no pitch signal to the PCC 19 when the SLC 11 is in a neutral pitch position.

If automatic pitch compensation for reverse pitch is required, an additional compensating relay valve (not shown) is provided in the reverse pitch circuit and receives air at pilot pressurefrom the accumulator tank similarly to the circuit of the forward pitch line line.

AUTOMATIC PITCH COMPENSATORS means 41 can be connected to the fuel rack, since the fuel rack responds to rpm changes, at constant rack setting.

Hereinafter and in the claims all connections to detect governor response, whether coupled to output from the governor or to the fuel rack or equivalent, are referred to as being coupled to governor output.

The mechanism 36.2 and the, coupling 41 are hereinafter referredto as a governor to regulating valve coupling, GRVC, being means transmitting governor response to the CAPRV so changing output pilot pressure at the port 34. This controls fuel supply, as ex plained, tending to maintain predetermined rpm.

The three APC embodiments described have respectively mechanical servo and hydraulically actuated GRVCs. Details of each are described below with reference respectively to FIGS. 2 and 3, 4 and 5, and 6 and 7, operation of each being separately described in a detail description following.

Each APC embodiment includes the known CAPRV and a mechanical servo or hydraulic GRVC, selection of a particular GRVC being dependent on governor output as will be explained. FIGS. 2 and 3, mechanical APC A mechanically actuated automatic pitch compensator 50, hereinafter APC 50 includes a CAPRV 51 with outlet inlet and exhaust ports 51.1, 51.2, 51.3 and a GRVC 52.

The APC 50 is connected to an engine rpm control device by means generally similar to the means 41 of FIG. 1, and includes means, namely a hinged lever 55 mechanically linked to the fuel rack of an engine or the governor output shaft. A series of holes 56 is provided at an outer end 57 of the lever 55 to permit matching of characteristics of the hydraulic circuit with characteristics of the engine and governor.

The lever 55 has an outer end 57 and an inner end "61, and is hinged for rotation on a pin 59, the end 61 is closer to the pin than the end 57. The pin 59 is carried in hinge mounts 63 and 65 best seen in FIG. 3, and screw adjustment means 66 at the end 61 are in contact with an outer end of a pushrod 67 of the APC 50, the pushrod being urged outwards against the end 61.

A relatively large movement of the outer end 57 in a direction shown by an arrow 69 results in a comparatively small movement of the screw adjusting means 66, and with it the pushrod 67, in a direction shown. by an arrow 71. The pushrod 67 -is a metering activation means, movement of the pushrod actuating metering means within the CAPRV 36.1, the metering means producing a change in pilot pressure from the outlet port 51.1. In an equilibrium position, at constant fuel flow to theengine, there is no movement of the lever 55.

The mechanism described including the coupling means is thus means, responsive to'governor output, i.e. to change in rpm, to operate the metering activation means 67 of the CAPRV 36.1, and serves as the mechanical GRVC 52 as aforesaid.

Compensating air pressure regulating valve The CAPRV 51 functions essentially as the CRV 23 in that a metering means within the valve meters inlet air pressure producing an outlet pressure lower than inlet pressure, excess air being exhausted through the exhaust port. This valve which, as stated, is common to all the APCs described, being well known, is not described in detail. Any type of CAPRV having characteristics above is suitable, namely having means to meter inlet pressure so as to produce a lower outlet pressure. For all the CAPRVs herein, extension of the end of the pushrod 67 decreases pilot pressure and the APC is coupled to the rpm control device, i.e. governor output, so that a demand for more fuel extends the end of the pushrod 67.

The inlet and outlet ports 51.2 and 51.1 of the CAPRV have common flow control needle valves (not shown), the valves controlling the volume flow of air entering and leaving the APC 50. Relative settings of the needle valves permit adjustment of response characteristics of the PCC 19, particularly so as to reduce chance of the engine being overloaded following a sudden increase in load. Commonly the needle valve is a tapered needle axially adjustable of a metering bore, and serves as a means to adjust response of the system.

FIGS. 4 and 5, servo operated APC A servo operated automatic pitch compensator 80, hereinafter APC 80, has the CAPRV 36.1 substantially as before described and a GRVC designated generally 36.2. The inlet and outlet ports 38 and 34 are provided with flow control needle valves as before.

The CAPRV 36.1 is operated by a pushrod 86 having a cam follower roller 87 at a lower end as shown, the pushrod 86 being a metering activation means of the CAPRV 36.1. The roller 87 rolls on a cam face 88 of a cam 89, the cam 89 being mounted on a left hand end, (as seen in FIG. 4) of an actuating rod 91. The rod 91 is aligned with a central axis of a cylinder 92, the cylinder having a cylindrical inner wall 94, and an outer end cap 96 at a right hand end. A right hand end wall 97 of a cam housing, generally 98, provides a left hand closer or inner end wall of the cylinder and the actuating rod 91 is free to slide in a bore 99 passing through the end wall 97.

A coupling means generally 102, functions as the means 41 in FIG. 9, being connected to an engine rpm control device. The means 102 has a cranked lever 103 having an upper arm 104, an inner end 105 of the arm 104 being secured by pinch bolt means 107 to a rotatable pin 108. An outer end 106 of the arm 104 is mechanically linked to a fuel rack or governor output shaft of the engine, a series of holes 109 being provided for matching as before. The pin 108 is journalled in bearings 111 and 112 and a lower arm 113 has an inner end 114 secured by screw means 115 (FIG. 5 only) to the pin 108. Screw adjusting means 119 are provided at an outer end 118 of the arm 113 and contacts a right hand end 121 of a control rod 122 which rod is free to slide axially in a bore 123 in the end cap 96.

Undesignated seals are provided to stop material leakage between the rods 91 and 122 and the bores above, and leakage between joins of the cylinder 92 and the end cap and cam housing. Rotation of the upper arm 104 in a direction shown by an arrow 120 results in axial translation of the control rod 122 in the direction shown by an arrow 124.

Two axial studs 125 and 126 (P16. only) are used to retain brackets for the bearing housings 111 and 112, and two further similar studs, (one only being shown designated 127) are used to secure the right hand end cap to the cylinder. An oil inlet port 131, integral with the cam housing 98 is connected by hose (not shown) to an oil outlet port from the engine (not shown) and receives engine oil under pressure. An oil outlet port 132 is provided on the right hand end of cap 96 and is connected to an engine oil sump (not shown) by a scavenge hose (not shown).

The control rod 122 has a mid-portion 134 of reduced diameter defined in part by a right hand shoulder 135 and a left hand shoulder 136, the shoulder 136 being shown in broken outline. A plug 137 is provided at the left hand end of the control rod 122, the shoulder 136 being a right hand end of the plug. The plug 137 and a portion of the reduced portion 134 are fitted within a blind bore 139 of the actuating rod 91, sufficient clearance being provided around the plug 137 to permit free sliding of the plug within the bore 139. A port 141 passes through the rod 91 to the blind bore 139.

A piston 143 is secured on a right hand end of the rod 91 on a side of the port 141 remote from the cam 89. Thus the cylinder 92 is divided into two spaces, namely an or left cylinder space 144 defined in part by the piston and end wall 97 and communicating with the inlet port, and an outer space 145 defined in part by a right hand end of the blind bore 139 and the end cap 96, and communicating with the outlet port 132. An annular passage 142 (broken outline) is defined by the portion of reduced diameter and the bore 139 and extends between the port 141 and the outer space 145. The bore 139, hereinafter the control bore, and the port 141, hereinafter the control port, communicate the space 144 with the space 145 through the annular passage 142. In an equilibrium position at constant fuel flow to the engine, engine oil flow through the annular passage 142 is restricted at a left hand end by the plug 137 partially blocking the control port 141.

A first compression spring 147 is provided in the right hand cylinder space 145 and is compressed between the piston 143 and a left hand face of the right hand end cap 96. Thus the spring 147 forces the piston and end cap apart. A second compression spring 149 is compressed between the piston 143 and the shoulder 135. This spring has a truncated-conical section and urges the control rod 122 outwards from the control bore 139. Spring clips 151 and 152 serving as stops are provided at positions on the control rod 122 to restrict movement of the rod 122.

A passage (not shown) connects the oil outlet port 132 with the right hand cylinder space 145 to provide means to scavenge oil from the space 145. A radially disposed bleed passage 154 on the right hand side of the shoulder 136 communicates with an axial bleed passage (not shown) which extends leftwards communicating with the blind end of the bore 139, the bleed passages above, hereinafter bleed means, are to prevent a hydraulic lock at the blind end of the bore 139. Other means to prevent hydraulic locks are known. The hydraulic cylinder assembly including the activating and control rods 91, 122, the cam 89, and the coupling means 102 is designated generally 36.2 and is seen to constitute servo means responsive to governor output, i.e. responsive to rpm change, to operate the CAPRV 36.1 as aforesaid, and thus serves as the servo GVRC 36.2. FIGS. 6 and 7, hydraulic APC A hydraulically-actuated automatic pitch compensator hereinafter APC 160, includes a CAPRV 161 and a GRVC 162. The CAPRV has inlet port 163, an outlet port 164, and an exhaust port 165, positions of which are shown in broken outline. For reasons which are later explained, these inlet and outlet ports are not provided with flow control needle valves thus contrasting with the CAPRV 51 (FIG. 2) and the CAPRV 36.1 (FIG. 4).

The CAPRV 161 is secured to a cam housing 166 of a cylinder 168. The cylinder 168 has an end cap 169 at a right hand end and has a left hand end closed by a right hand end wall 171 of the cam housing 166. The end wall 171 has a bore 172 in which an actuating rod 174 is a sliding fit. The rod 174 has an outer end 175 to which a piston 176 is secured, and an inner end 177 to which a cam 178 is secured. The piston 176 divides the cylinder 168 into two spaces, a left hand cylinder space 187 and a right hand cylinder space 188. The cam 178 has a cam follower 179 on an end 181 of a push rod of the CAPRV 161, the cam and operation of the CAPRV 161 being similar to that as described with reference to FIGS. 2 and 4. Thus movement of the piston in a direction shown by an arrow permits the cam follower to extend from the CAPRV 161 in response to a demand to decrease pitch by decreasing pilot pressure.

The end cap 169 is secured to the cylinder 168 by studs, two being designated 182 and 183. Ports 185 and 186 communicate with pressure output ports from an engine governor (not shown) through hydraulic hoses (not shown) and, in an equilibrium position at constant fuel flow delivery, the output ports of the governor are closed and there is no fluid flow to or from the cylinder 168, the piston 176 being hydraulically locked within the cylinder. Output connections from the governor are such that, from an equilibrium position, a demand from the governor to decrease fuel flow to the engine results in additional oil being fed into the port 185 into the space 187, the piston moving to the right and scavenging oil from the space 188, returning it to the governor through the port 186. For an increase in fuel to the engine, flow directions are reversed, the piston then moving to the left in the direction of the arrow 180.

Governor oil pressure and cross-sectional area of the piston 176 are such that pressure difference across the piston is sufficient to move the actuating shaft 174 against resistances inherent in pistons and cylinders.

The mechanism above described, including the cylinder, piston rod, piston, and cam and hydraulic hoses (not shown) to the governor, is designated generally 162 in FIG. 6. The mechanism is thus seen to be hydraulic means responsive to difference in pressure, i.e., to rpm change, to operate the CAPRV 161 as aforesaid, and thus serves as the hydraulic GRVC 162. FIG. 8 and reference to FIG. 6

A biased flow needle valve 221 is fitted to the port 185 of the hydraulically actuated APC 160, FIG. 6, to provide a means of rapid scavenging of the space 187, reducing chance of overloading the engine by increasing speed of response of compensation. The port 185 FIG. 8 has a threaded counter-bored passage 222 to accept a coupling at one end of the hydraulic hose. from the governor, fluid from the bore entering the valve 221 in a direction shown by an arrow 223. A metering bore 225 extends from the passage 222 and has a metering port 226 as shown communicating with a threaded passage 224. A needle valve stem 227 threadedin the passage 224 can be turned by a knurled end 229, and has a conical end 228 which cooperates with the port 226 so that axial movement of the end 228 controls volume flow of fluid through the port 226. An infeed passage 231 extends from the metering port 226, which when the port 226 is open, feeds fluid into the APC 60 in a direction shown by an arrow 232.

A ball valve 234 is provided to permit a rapid drop of pressure in the CAPRV 161 (FIG. 6) to reduce chance of overloading should a sudden increase in load on the engine occur. The valve 234 has a ball 235 urged against a valve seat 236 by a spring 237 augmented by fluid pressure within the bore 225. Thus, if fluid pressure within the space 187 exerts aforce on the ball 235 less than the force of the spring 237 plus fluid pressure within the bore 225, the valve remains closed.

A rapid increase in load on the engine causes the governor to make a sudden demand to increase fuel. With reference to FIG. 6, fluid is fed rapidly into the port 186 with a corresponding rapid increase in pressure in the space 187. There is a sudden force on the ball 235 urging it to the right, which overcomes the force of the spring 237 and pressure in the bore 225, moving the ball in a direction shown by the arrow 239. Fluid from the space 187 is exhausted mainly through the valve 234, a portion-passing the needle valve 221. Passage of fluid in a direction shown by the arrow 239 is several orders of magnitude greater than that through the needle valve 221, providing relatively rapid response of the APC 160 to a sudden demand for more fuel. This results in correspondingly rapid pitch reduction.

Thus the needle valve and ball valve assembly, designated generally 240 in FIG. 8, serve as a means of increasing speed of response of the APC in one direction, namely in the direction of pitch reduction, to

. produce a rapid change in pitch of the propeller to reduce load. Providing the valve 221 in the port 185 produces a more rapid response of the APC than would be obtained by fitting needle valves in the ports 163 and 164 of the CAPRV 161. Thus the APC 160 more effectively safeguards the engine against overload In practice a second biased flow needle valve similar to the valve 221 can be fitted to the port 186 for simplicity ofinstallation of the component.

Selection of APC The APC 36 shown in FIGS. 1 and 9 is similar to the APC described with reference to FIGS. 4 and 5. Selection of a particular APC is dependent on governor output characteristics which themselves are dependent on type of governor used and size of the engine being governed. Thus, depending on the governor, the GRVC selected can be that as shown in the APC S0 in FIG. 2 or as the APC as described in FIG. 6.

Selection of Governor A type of governor as used in diesel/electric locomotives and manufactured by Woodward or Regulator Europa has been found satisfactory for use with the circuit of FIG. 1. A Woodward PGL governor has been found adequate when the governor output is coupled conventionally to the engine and also to the coupling means of the APC. The governor output is one of two types: an output shaft which rotates through 30 to 40 degrees from minimum to maximum speed settings and is controlled by the governor input, or can be two ports which provide a fluid pressure difference. The outputs above are connected to fuel delivery means of the engine, usually the fuel rack. With the first type of governor output, with no demand to change fuel delivery, the output shaft is stationary. With the second type of governor, with no demand to change fuel delivery, fluid flow to and from the governor ports is zero.

The APC 50 is used only with governors having a relatively high torque at the output shaft, as rotation of the lever 55 results in work to overcome resistances. Some governors have an output shaft torque insufficient to operate the APC 50 without reducing effectiveness of the governor; these require the APC 80, wherein the lever 103 takes relatively little work from the governor due to servo-action of the control rod 122 and the actuating rod 91, as below described. In such a mechanism a small force on the control rod 122, which acts as a master controls a larger force on the actuating rod 91, the slave. When using hydraulic pressure outputs of a governor, the APC 160 is described in FIG. 6 is used. Different sizes of piston can be used to accomodate relative pressure differences encountered with this type of governor.

Thus governor output determines selection of APC so that the GRVC thereof is compatible with governor output.

OPERATION FIGS. 1 and 9, pneumatic circuit generally FIG. 9 shows the FIG. 1 schematic hydraulic circuit with relevant components diagrammatically shown operatively connected to an engine governor and to a variable pitch propeller of a vessel.

With prior art circuits without automatic pitch compensation, the SLC 11 controls pitch and throttle concurrently. With the vessel stationary and the engine idling, the propeller is at neutral pitch. A manually imparted signal to the SLC 11 by movement of the lever 12 adjusts relative metering of air through the control valves 13, 14, and 15. From neutral pitch rotation of the lever increases pitch to approximately forty percent of full pitch, whilst the engine remains at idle. With further rotation of the lever 12,.engine rpm increases concurrently with pitch until approximately eighty percent of maximum is attained. Still further rotation of the lever 12 increases engine rpm to one hundred percent, the pitch remaining at one hundred percent. With an automatic reverse pitch (not shown) the ratios above apply to the reverse pitch condition also, reverse pitch being accomplished by rotating the lever in an opposite direction. If a two lever control were used, as stated previously, pitch and throttle are controlled independently.

Using an automatic pitch compensated circuit according to the invention, if there is no demand from the governor for a change in fuel the coupling means 41 of the APC 36 is stationary and the APC 36 is in an equilibrium condition such that output pilot pressure from the AFC 36 is constant.

With a vessel cruising at a speed and engine rpm both below maximum, an increase in load on the engine produces a signal from the governor to increase fuel delivery to the engine to maintain pre-set engine rpm. Without pitch compensation by the APC 36 an increase in load on the engine would produce too coarse a pitch condition causing an over-fueling of the engine, with the engine trying to accelerate in response to the over-fueling. The engine would thus labor undesirably for a period dependent on acceleration of the vessel.

With automatic pitch compensation, a typical sequence of events to correct a condition of too coarse pitch is as follows:

1. The propeller, running at too coarse a pitch, causes the engine rpm to decrease below the rpm preset by the governor.

2. The governor rapidly responds by moving the fuel rack to increase fuel delivery to the engine, to increase rpm to attain that pre-set by the governor. This action is rapid, decrease of a few revolutions per minute sufflces to cause the sequence above.

3. Movement of the fuel rack to increase fuel actuates the APC 36, which compensates for too coarse a pitch by decreasing the pitch.

4. A decreased pitch at the increased fuel delivery results in a small increase in rpm in increase less than the decrease in (1) above.

5. Increase in rpm is rapidly corrected by the governor, which reduces fuel delivery by a small amount, a smaller decrease than the increase in (2) above.

6. Decrease in fuel delivery causes a small increase in pitch, much smaller than the decrease in pitch above.

7. Thus by a series of successive approximations and minor overcorrections, the pitch of the propeller is adjusted to maintain essentially constant fuel delivery to the engine. The above sequence of events occupies a few seconds, or less depending on the compensation required. Fluctuation of the rpm from the pre-set rpm is typically in a range of one or two revolutions per minute, depending on response of the governor. The return to the pre-set rpm can be likened to an asymptotic approach to an equilibrium position ofa dampened vibrating system.

Maximum compensation of pitch occurs when the pilot pressure from the APC is at its lowest namely pressure at the port 29 of the CRV 23 being about one half of maximum value of pilot pressure, as read at gauge. This is termed 50 percent compensation. The maximum compensation above is rarely reached, a more usual compensation being about 35 percent, which generally occurs at about 80 percent engine rpm.

In the following description of operation, only the initial change in pitch is described, not the successive approximations above.

FIGS. 2 and 3, alternative A demand from the governor to change fuel delivery rotates the lever 55 about the pin 59 so that the end of the pushrod 67 moves in or out of the CAPRV 51 of the APC 50.

If there is a sudden increase in load on the engine, the governor responds to increase fuel to maintain preset rpm, so the fuel rack moves to increase fuel delivery and also rotates the lever 55 in the direction shown by the arrow 69. The outlet pressure (ie pilot pressure) from the APC 50 is thus decreased and, is fed to the CRV 23 via the accumulator tank 31. A decrease in pilot pressure decreases output pressure from the CRV 23 and the PCC 19 experiences a drop in forward pitch pressure, this reduces forward pitch. The demand to reduce forward pitch is experienced by the PCC 19 without additional movement of the lever 12. Thus reduction in pitch is fully automatic, the APC having sensed a demand for more fuel to maintain the rpm at that pre-set by the governor.

Load compensation for the APC 50 is about ninety percent, so that the engine tends to be somewhat overloaded with any sudden increase in load. Drop in power output from the engine due to, for instance, failure of perhaps two out of six cylinders of the engine causes the fuel rack to move to a new position to supply more fuel in an attempt to maintain the pre-set rpm. Such new position will result in over fueling the remaining operative cylinders, somewhat tending to overload the engine.

FIGS. 4 and 5, alternative At a constant fuel delivery, the APC 81 is in an equilibrium position and the lever 102 is stationary. Lubricating oil from the engine is fed into the port 131 essentially under constant pressure independent of engine rpm, and produces a force to the right on the piston 143, which force is counteracted by fluid forces in the cylinder combined with forces from the springs 147 and 149.

Oil flows into the left hand cylinder 144 and leaves the cylinder through the control port 141, flowing along the annular passage 142 into the space 145. The right hand end of the plug 137 partially blocks the control port 141 and meters oil flow from the cylinder space 144, thus reducing oil pressure in the space 145 from that in the space 144. Relative positions of the plug 137 and the bore 141 are dependent mainly on viscosity and pressure of the oil, spring forces, and diameter of the piston. When there is constant fuel delivery to the engine, relative positions of the plug 137 and the control port 141 do not change being at an equilibrium position thus under this condition the piston does not move within the cylinder.

A sudden increase in load on the engine produces a demand from the governor to increase fuel, the fuel rack moving to increase the supply of fuel to the engine. The upper arm 104 of the coupling means 102, being connected to the fuel rack, moves in the direction of the arrow 120, the screw adjusting means 119 pushing the control rod 122 to the left into the cylinder. Thus the plug 137 is moved to the left, reducing the restriction of flow at the control port 141 and increasing flow of oil from the space 144 through the annular passage 142 into the the right hand space 145; oil pressure in the space 145 being higher than before movement of the plug because of less metering at the port 141. I Y

An increase inp'ressure in the space 145 forces the piston to the left, and,'as the plug 137 remains stationary relative to the APC 80, the port 141 againbecomes restricted by the plug 137. Increased restriction of the control port 141 reduces pressure in the space 145 and movement of the piston 143 ceases, the piston attaining a new equilibrium position somewhat to the left of the original position until there is further movement of the coupling means102.

Movement of the piston 143 to the left moves the cam 89, to the left, causing the cam follower 87 to roll down the cam face 88, with the pushrod end 86 moving outwards of the CAPRV 81. Effect of the metering means within the CAPRV 81 is thus changed, extension of the end of the pushrod 86 rjeducingpilot pressure which in turn modifies the demand on the forward pitch port PCC 19 to a reduced forward pitch of the propeller.

A sudden decrease in load on the engine, results in a demand from the governor for less fuel to be delivered to the engine, resulting in movement of the coupling means 102 in the direction opposite to that of arrow 120, thus moving the screw adjusting means 119 away from the end 121 of the rod 122. The spring 149 urges the rod 122 outwards and thus the plug 137 increases metering at the port 141, which metering decreases the pressure in the space 145 relative to the space 144. Thus the piston 143 moves to the right, such movement of the piston decreasing metering at the port 141. This increases pressure in the space 145 and stops the movement of the piston 143, thus it attains a new equilibrium position to the right of theprevious equilibrium posi tion. This new equilibrium position is maintained until there is a further change in fuel delivery to the engine.

Movement of the piston 143 to the right results in a corresponding movementof the cam 89, forcing the cam follower upwards and, with it, the end of the pushrod 86, into the CAPRV 81, increasing pilot pressure output from the APC. This results in an increase in output pressure from the CRV 23 increasing the original forward pitch and reducing rpm of the engine. FIGS. 6 and 7, alternative With reference to the operation of the APC 160, in an overload condition, a demand from the governor to increase fuel supply to the engine causes fluid from the governor output to be fed into the port 186. Fluid is scavenged from the port 185 as the pistonl76 is forced to the left, and the pushrod. is extended from the CAPRV 161, reducing pilot pressure and therefore reducing forward pitch. I

An opposite demand from the governor to decrease fuel to the engine results also. in increased'pitch as follows. Fluid from the governor output is fed into the port 185 and scavenged from the port 186, thus resulting in movement of the piston 176 to the right, this causes the cam follower 179 to move the pushrod end into the CAPRV 161, increasing pilot pressure. Thus there is asignal from CRV 23 to the PCC 19 to increase pitch.

Response of the APC is dependent'on many factors and is adjustable by means of the biased flow nee dle valves fitted at the ports and 186, operation of which are described with reference to FlG..8.

FIG. 8

When setting up a circuit using the APC 160, the governor output characteristics are matched to the engine characteristics and response of the CAPRV 161 by the needle valves incorporated into the outlet and inlet ports of the APC 160.

Operation of the biased flow needlevalve 22 lat the port 185 of the APC 161 is as follows, operation of the second biased, flow needle valve being within this description. Fluid from the governor'output enters the inlet port 51 thorugh the metering bore 225 and volume of flow is controlled by position of the conical end 228 of the needle, valve stem 227 relative to the metering port 226. Metered fluid from the port 226 passes through the infeed passage 231 in the direction shown by the arrow 232 into the space 187 (FIG. 6).

The overload ball valve 234 is closed as fluid pressure difference between the fluid in the space 187 and the fluid in the bore 225 is below a predetermined value.

p A sudden increase in the pressure difference above may exceed the predetermined value above which results in opening of the valve 234, fluid from the space 187 passing the ball 235 into the metering bore 225.

Other factors being constant, fluid flow through the ball valve 234 is several orders of magnitude greater than the flow through infeed passage 231, permitting relatively rapid decrease in fluid pressure in the space 187 increasing response of APC 160 by increasing speed of exhaust of the cylinder spaces.

FIG. 1 General summary of operation Thus summarizing the operation of the three embodiments of the APCs described, a change in fuel delivery disturbs the equilibrium position of the APC which adjusts the metering means within the CAPRV of the APC. Thus pilot pressure is changed, which pressure affects the compensation of the output pressure from the CRV 23. Degree of compensation of the output pressure from the CRV 23 controls final pitch selected by the PCC 19.

lclaim:

1. An automatic pitch compensator adapted for the use in a pneumaticallyoperated control circuit in a marine vessel having an engine, rpm of the engine being selected by a speed setting of a governor, the governor having an output reflecting governor response coupled to an engine rpm control device to regulate engine rpm, the engine powering a controllable pitch propeller; the automatic pitch compensator including:

a. a compensating air pressure regulating valve (CAPRV) with an inlet port, an outlet port and an exhaust port, the valve having a metering means adapted to meter air under pressure received in the inlet port to a pilot pressure at the output port, the metering means being operably by a metering activation means,

. a governor to regulating valve coupling (GRVC) connecting the metering activation means of the compensating air pressure regulating valve to the governor output so as to transmit governor response to the metering means,

so that change in engine rpm from governor set rpm is reflected in governor output, which change is transmitted to the metering activation means of the compensating air pressure regulating valve, so that metering of air pressure fed into the input port of the compensating air pressure regulating valve is changed so as to change pilot pressure in an amount proportional to change in engine rpm from governor set rpm.

2. An automatic pitch compensator as defined in claim 1 adapted for use with a governor having a mechanical output, in which the governor to regulating valve coupling includes: a

c. a coupling means operatively connected to the governor output,

d. a servo means responsive to governor output to transmit governor response to the metering activation means, to operate the compensating air pressure regulating valve.

3. An automatic pitch compensator as defined in claim 2, in which the servo means includes:

e. a cylinder having inner and outer end walls, an oil inlet port adapted to receive oil under pressure, and an oil outlet port adapted to return oil to a sump,

f. a control rod slidable within the cylinder, the control rod having an outer end in engagement with the coupling means to receive governor response, an inner end having a plug, and a portion of reduced diameter,

. an actuating rod aligned with, and adapted to slide axially relative to, the control rod, the actuating rod having an inner end cooperating with the metering activation means of the compensating air pressure regulating valve so that axial sliding of the actuating rod relative to the cylinder changes output from the compensating air pressure regulating valve, the actuating rod having an outer end having a control bore accepting the plug at the inner the control rod, the actuating rod having an inner end cooperating with the metering activation means of the compensating air pressure regulating valve so that axial sliding of the actuating rod relative to the cylinder changes output from the compensating air pressure regulating valve, the actuating rod having an end of the control rod, and a control port communicating with the control bore, an annular passage being defined by the portion of reduced diameter and the control bore and extending between the control port and the outer end of the actuating rod, the actuating rod further including a bleed means to scavenge oil from the control bore to prevent a hydraulic lock forming within the control bore, a piston secured adjacent the outer end of the actuating rod on a side of the control port remote from the inner end of the actuating rod, the piston dividing the cylinder into inner and outer cylinder spaces, the inlet port communicating with the inner cylinder space and the outlet port communicating with the outer cylinder space,

i. a first compression spring extending between the piston and the outer end wall of the cylinder so as to urge the piston away from the cylinder,

j. a second compression spring extending between the piston and the control rod so as to urge the inner end of the control rod away from the control bore of the actuating rod, relative disposition of the plug and the control bore being such that the plug partially blocks the control port, so that oil leaving the inner cylinder space passes through the control port, is metered by restriction at the control port, and passes at a reduced pressure along the annular passage into the outer cylinder space to leave the outer cylinder space through the outlet port, the oil in the outer cylinder space producing a force on the piston to combine with the spring forces in opposition to force from oil pressure in the inner cylinder space, so that in an equilibrium position force on the piston from oil in the inner cylinder equals force on the piston from oil in the outer cylinder plus force from the springs so that the piston is stationary relative to the cylinder; and movement of the coupling means resulting from a change in engine load moves the control rod relative to the actuating rod thus changing the metering of the oil flow and producing a force difference on the piston thus disturbing the equilibrium and moving the piston in a direction to regain the equilibrium position, movement of the piston moving the actuating rod axially so as to change position of the metering activation means thus altering pilot pressure at the output port in an amount proportional to change in engine load.

4. An automatic pitch compensator as defined in claim 3 in which the coupling means includes:

k. a lever having an upper arm adapted to be linked to the output of the governor, and a lower arm, the lever being hinged for rotation relative to the automatic pitch compensator, I

l. screw adjusting means provided at the outer end of the lower arm, the means contacting an outer end of the control rod so as to transmit governor response to the control rod and to provide adjustment of the coupling means.

5. An automatic pitch compensator as defined in claim 3 in which:

m. the mid portion of reduced diameter is defined in part by a shoulder adjacent the inner end, the shoulder adapted to serve as a metering means when adjacent the control port.

6. An automatic pitch compensator as defined in claim 2 in which:

n. inlet and outlet ports of the compensating air pressure regulating valve includes flow control needle valves to permit adjustment of response of the automatic pitch compensator.

7. A pneumatically operated control circuit adapted for use in a marine vessel powered by an engine, rpm of the engine being selected by a speed setting of a governor, the governor having an output reflecting governor response coupled to an engine rpm control device to regulate engine rpm, the engine powering a controllable pitch propeller, the pneumatic circuit including:

a. a manual control (SLC) receiving air under pressure from a source, the control having valves communicating with a forward pitch line, a reverse pitch line and a throttle line, the valves being operable by an operator so as to selectively meter outputs to each line,

b. a pitch control cylinder (PCC) having a forward pitch port and a reverse pitch port, output from the pitch control cylinder being operatively connected to a pitch changing mechanism of the controllable pitch propeller, the reverse pitch line communicating with the reverse pitch port,

c. a throttle control (TC) having an inlet port connected to the throttle line, and an output connected so as to control the governor speed setting,

d. a compensating relay valve (CRV) having an inlet port, an outlet port, and a pilot pressure input port, the compensating relay valve having a metering means provided between the inlet port and the outlet port, the metering means being-activated by pilot pressure at the input port, the inlet port communicating with the forward pitch line and the outlet port communicating through a line with the forward pitch port of the pitch control cylinder,

e. an automatic pitch compensator (APC) having an inlet port accepting air under pressure from the supply, an outlet port discharging air at pilot pressure to the pilot pressure input port of the compensating relay valve, and an exhaust pipe to exhaust excess air to waste, theautomatic pitch compensator having I i. a compensating air pressure regulating valve (CAPRV) having a metering means between the inlet and outlet ports, and a metering activation means actuating the metering means,

a governor to regulating valve coupling (GRVC) connecting the metering activation means to the governor output so as to transmit governor response to the compensating air pressure regulating valve so as to change output pilot pressure at the outlet port, the governor response being dependent on load in the engine, f. an accumulator tank in series with the outlet port of the automatic pitch compensator and the input port of the compensating relay valve, so that a pitch signal of a manually imparted signal at the manual control to attain a perdetermined rpm and pitch is modified by a demand from the governor output dependent on load experienced by the engine, the modification altering the manually selected pitch so as to tend to maintain constant rpm.

8. A' pneumatically operated control circuit as defined in claim 7, in i which the governor has a mechanical output and the governor to regulating valve coupling includes:

g. a coupling means cooperatively connected to the governor output,

h. a servo responsive to governor output to transmit governor response to the metering activation means to operate the compensating air pressure regulating valve.

9. A pneumatically operated circuit as defined in claim 8 in whichthe servo means includes:

i. a cylinder having inner and outer end walls, an oil inlet port adapted to receive oil under pressure, and'an oil outlet port adapted to return oil to a sump,

j. a control rod slidable within the cylinder, the control rod having an outer end in engagement with the coupling means to receive governor response, an inner end having a plug, and a portion of reduced diameter,

k. an actuating rod aligned with, and adapted to slide axially relative to, the control rod, the actuating rod having an inner end cooperating with the metering activation means of the compensating air pressure regulating valve so that axial sliding of the actuating rod relative to the cylinder changes output from the compensating air pressure regulating valve, the actuating rod having an outer end having a control bore accepting the plug at the inner end of the control rod, and a control port communicating with the control bore, an annular passage being defined by the portion of reduced diameter and the control bore and extending between the control port and the outer end of the actuating rod, the actuating rod further including a bleed means to scavenge oil from the control bore to prevent a hydraulic lock forming within the control bore,

l. a piston secured adjacent the outer end of the actuating rod on a side of the control port remote from the inner end of the actuating rod, the piston dividing the cylinder into inner and outer cylinder spaces, the inlet port communicating with the inner cylinder space and the outlet port communicating with the outer cylinder space,

In. a first compression spring extending between the piston and the outer end wall of the cylinder so as to urge the piston away from the cylinder,

n. a second compression spring extending between the piston and the control rod so as to urge the inner end of the control rod away from the central bore of the actuating rod,

relative disposition of the plug and the control bore being such that the plug partially blocks the control port, so that oil leaving the inner cylinder space passes through the control port, is metered by restriction at the control port, and passes at a reduced pressure along the annular passage into the outer cylinder space to leave the outer cylinder space through the outlet port, the oil in the outer cylinder space producing a force on the piston to combine with the spring forces in opposition to force from oil pressure in the inner cylinder space, so that in an equilibrium position force on the piston from oil in the inner cylinder equals force on the piston from oil in the outer cylinder plus force from the springs so that the piston is stationary relative to the cylinder; and movement of the coupling means resulting from a change in engine load moves the control rod relative to the actuating rod thus changing the metering of the oil flow and producing a force difference on the piston thus disturbing the equilibrium and moving the piston in a direction to regain the equilibrium position, movement of the piston moving the actuating rod axially so as to change position of the metering activation means thus altering pilot pressure at the output port in an amount proportional to change in engine load.

10. An automatic pitch compensator as defined in claim 1 in which the governor has a mechanical output and in which the governor to regulating valve coupling includes:

0. a lever having an outer end adapted to be linked to the output of the governor and an inner end contacting and metering activation means of the compensating air pressure regulating valve, the lever being hinged for rotation relative to the automatic pitch compensator so that movement of the governor output is transmitted to the metering activation means.

11. An automatic pitch compensator as defined in r. a piston provided at the outer end of the actuating claim 1 adapted for use with a governor having hydraurod, the piston dividing the cylinder into cylinder he Output P whlch the f to regulating spaced on either the side of the piston, a port comvalve coupling includes a hydraulic means responsive municating with each Space, so that in response to to difference in pressure in the governor outputs, the 5 governor demand fluid flowing out of one govep hydrauhc means mch'dmg: nor output enters one port into one cylinder space p. a cylinder having closed ends, a port being provided adjacent each end with each port communicating with a respective port of the governor outputs,

q an actuating rod having inner and outer ends, the

rod being a sliding fit in a bore at one end of the cylinder, the inner end of the rod cooperating with the metering activation means of the compensating air pressure regulating valve, l5

and displaces the piston within the cylinder, fluid being scavenged from the other cylinder space through the other port, movement of the piston actuating the metering activation means of the compensating air pressure regulating valve so as to change pilot pressure in an amount proportional to governor response. 

1. An automatic pitch compensator adapted for the use in a pneumatically operated control circuit in a marine vessel having an engine, rpm of the engine being selected by a speed setting of a governor, the governor having an output reflecting governor response coupled to an engine rpm control device to regulate engine rpm, the engine powering a controllable pitch propeller; the automatic pitch compensator including: a. a compensating air pressure regulating valve (CAPRV) with an inlet port, an outlet port and an exhaust port, the valve having a metering means adapted to meter air under pressure received in the inlet port to a pilot pressure at the output port, the metering means being operably by a metering activation means, b. a governor to regulating valve coupling (GRVC) connecting the metering activation means of the compensating air pressure regulating valve to the governor output so as to transmit governor response to the metering means, so that change in engine rpm from governor set rpm is reflected in governor output, which change is transmitted to the metering activation means of the compensating air pressure regulating valve, so that metering of air pressure fed into the input port of the compensating air pressure regulating valve is changed so as to change pilot pressure in an amount proportional to change in engine rpm from governor set rpm.
 2. An automatic pitch compensator as defined in claim 1 adapted for use with a governor having a mechanical output, in which the governor to regulating valve coupling includes: c. a coupling means operatively connected to the governor output, d. a servo means responsive to governor output to transmit governor response to the metering activation means, to operate the compensating air pressure regulating valve.
 3. An automatic pitch compensator as defined in claim 2, in which the servo means includes: e. a cylinder having inner and outer end walls, an oil inlet port adapted to receive oil under pressure, and an oil outlet port adapted to return oil to a sump, f. a control rod slidable within the cylinder, the control rod having an oUter end in engagement with the coupling means to receive governor response, an inner end having a plug, and a portion of reduced diameter, g. an actuating rod aligned with, and adapted to slide axially relative to, the control rod, the actuating rod having an inner end cooperating with the metering activation means of the compensating air pressure regulating valve so that axial sliding of the actuating rod relative to the cylinder changes output from the compensating air pressure regulating valve, the actuating rod having an outer end having a control bore accepting the plug at the inner the control rod, the actuating rod having an inner end cooperating with the metering activation means of the compensating air pressure regulating valve so that axial sliding of the actuating rod relative to the cylinder changes output from the compensating air pressure regulating valve, the actuating rod having an end of the control rod, and a control port communicating with the control bore, an annular passage being defined by the portion of reduced diameter and the control bore and extending between the control port and the outer end of the actuating rod, the actuating rod further including a bleed means to scavenge oil from the control bore to prevent a hydraulic lock forming within the control bore, h. a piston secured adjacent the outer end of the actuating rod on a side of the control port remote from the inner end of the actuating rod, the piston dividing the cylinder into inner and outer cylinder spaces, the inlet port communicating with the inner cylinder space and the outlet port communicating with the outer cylinder space, i. a first compression spring extending between the piston and the outer end wall of the cylinder so as to urge the piston away from the cylinder, j. a second compression spring extending between the piston and the control rod so as to urge the inner end of the control rod away from the control bore of the actuating rod, relative disposition of the plug and the control bore being such that the plug partially blocks the control port, so that oil leaving the inner cylinder space passes through the control port, is metered by restriction at the control port, and passes at a reduced pressure along the annular passage into the outer cylinder space to leave the outer cylinder space through the outlet port, the oil in the outer cylinder space producing a force on the piston to combine with the spring forces in opposition to force from oil pressure in the inner cylinder space, so that in an equilibrium position force on the piston from oil in the inner cylinder equals force on the piston from oil in the outer cylinder plus force from the springs so that the piston is stationary relative to the cylinder; and movement of the coupling means resulting from a change in engine load moves the control rod relative to the actuating rod thus changing the metering of the oil flow and producing a force difference on the piston thus disturbing the equilibrium and moving the piston in a direction to regain the equilibrium position, movement of the piston moving the actuating rod axially so as to change position of the metering activation means thus altering pilot pressure at the output port in an amount proportional to change in engine load.
 4. An automatic pitch compensator as defined in claim 3 in which the coupling means includes: k. a lever having an upper arm adapted to be linked to the output of the governor, and a lower arm, the lever being hinged for rotation relative to the automatic pitch compensator, l. screw adjusting means provided at the outer end of the lower arm, the means contacting an outer end of the control rod so as to transmit governor response to the control rod and to provide adjustment of the coupling means.
 5. An automatic pitch compensator as defined in claim 3 in which: m. the mid portion of reduced diameter is defined in part by a shoulder adjacent the inner end, the shoulder adapted to serve as a metering means whEn adjacent the control port.
 6. An automatic pitch compensator as defined in claim 2 in which: n. inlet and outlet ports of the compensating air pressure regulating valve includes flow control needle valves to permit adjustment of response of the automatic pitch compensator.
 7. A pneumatically operated control circuit adapted for use in a marine vessel powered by an engine, rpm of the engine being selected by a speed setting of a governor, the governor having an output reflecting governor response coupled to an engine rpm control device to regulate engine rpm, the engine powering a controllable pitch propeller, the pneumatic circuit including: a. a manual control (SLC) receiving air under pressure from a source, the control having valves communicating with a forward pitch line, a reverse pitch line and a throttle line, the valves being operable by an operator so as to selectively meter outputs to each line, b. a pitch control cylinder (PCC) having a forward pitch port and a reverse pitch port, output from the pitch control cylinder being operatively connected to a pitch changing mechanism of the controllable pitch propeller, the reverse pitch line communicating with the reverse pitch port, c. a throttle control (TC) having an inlet port connected to the throttle line, and an output connected so as to control the governor speed setting, d. a compensating relay valve (CRV) having an inlet port, an outlet port, and a pilot pressure input port, the compensating relay valve having a metering means provided between the inlet port and the outlet port, the metering means being activated by pilot pressure at the input port, the inlet port communicating with the forward pitch line and the outlet port communicating through a line with the forward pitch port of the pitch control cylinder, e. an automatic pitch compensator (APC) having an inlet port accepting air under pressure from the supply, an outlet port discharging air at pilot pressure to the pilot pressure input port of the compensating relay valve, and an exhaust pipe to exhaust excess air to waste, the automatic pitch compensator having i. a compensating air pressure regulating valve (CAPRV) having a metering means between the inlet and outlet ports, and a metering activation means actuating the metering means, ii. a governor to regulating valve coupling (GRVC) connecting the metering activation means to the governor output so as to transmit governor response to the compensating air pressure regulating valve so as to change output pilot pressure at the outlet port, the governor response being dependent on load in the engine, f. an accumulator tank in series with the outlet port of the automatic pitch compensator and the input port of the compensating relay valve, so that a pitch signal of a manually imparted signal at the manual control to attain a perdetermined rpm and pitch is modified by a demand from the governor output dependent on load experienced by the engine, the modification altering the manually selected pitch so as to tend to maintain constant rpm.
 8. A pneumatically operated control circuit as defined in claim 7, in which the governor has a mechanical output and the governor to regulating valve coupling includes: g. a coupling means cooperatively connected to the governor output, h. a servo responsive to governor output to transmit governor response to the metering activation means to operate the compensating air pressure regulating valve.
 9. A pneumatically operated circuit as defined in claim 8 in which the servo means includes: i. a cylinder having inner and outer end walls, an oil inlet port adapted to receive oil under pressure, and an oil outlet port adapted to return oil to a sump, j. a control rod slidable within the cylinder, the control rod having an outer end in engagement with the coupling means to receive governor response, an inner end having a plug, and a portion of reduced diameter, k. an actuating Rod aligned with, and adapted to slide axially relative to, the control rod, the actuating rod having an inner end cooperating with the metering activation means of the compensating air pressure regulating valve so that axial sliding of the actuating rod relative to the cylinder changes output from the compensating air pressure regulating valve, the actuating rod having an outer end having a control bore accepting the plug at the inner end of the control rod, and a control port communicating with the control bore, an annular passage being defined by the portion of reduced diameter and the control bore and extending between the control port and the outer end of the actuating rod, the actuating rod further including a bleed means to scavenge oil from the control bore to prevent a hydraulic lock forming within the control bore, l. a piston secured adjacent the outer end of the actuating rod on a side of the control port remote from the inner end of the actuating rod, the piston dividing the cylinder into inner and outer cylinder spaces, the inlet port communicating with the inner cylinder space and the outlet port communicating with the outer cylinder space, m. a first compression spring extending between the piston and the outer end wall of the cylinder so as to urge the piston away from the cylinder, n. a second compression spring extending between the piston and the control rod so as to urge the inner end of the control rod away from the central bore of the actuating rod, relative disposition of the plug and the control bore being such that the plug partially blocks the control port, so that oil leaving the inner cylinder space passes through the control port, is metered by restriction at the control port, and passes at a reduced pressure along the annular passage into the outer cylinder space to leave the outer cylinder space through the outlet port, the oil in the outer cylinder space producing a force on the piston to combine with the spring forces in opposition to force from oil pressure in the inner cylinder space, so that in an equilibrium position force on the piston from oil in the inner cylinder equals force on the piston from oil in the outer cylinder plus force from the springs so that the piston is stationary relative to the cylinder; and movement of the coupling means resulting from a change in engine load moves the control rod relative to the actuating rod thus changing the metering of the oil flow and producing a force difference on the piston thus disturbing the equilibrium and moving the piston in a direction to regain the equilibrium position, movement of the piston moving the actuating rod axially so as to change position of the metering activation means thus altering pilot pressure at the output port in an amount proportional to change in engine load.
 10. An automatic pitch compensator as defined in claim 1 in which the governor has a mechanical output and in which the governor to regulating valve coupling includes: o. a lever having an outer end adapted to be linked to the output of the governor and an inner end contacting and metering activation means of the compensating air pressure regulating valve, the lever being hinged for rotation relative to the automatic pitch compensator so that movement of the governor output is transmitted to the metering activation means.
 11. An automatic pitch compensator as defined in claim 1 adapted for use with a governor having hydraulic output ports in which the governor to regulating valve coupling includes a hydraulic means responsive to difference in pressure in the governor outputs, the hydraulic means including: p. a cylinder having closed ends, a port being provided adjacent each end with each port communicating with a respective port of the governor outputs, q. an actuating rod having inner and outer ends, the rod being a sliding fit in a bore at one end of the cylinder, the inner end of the rod cooperating with the metering activation means of the compensating air pressure reguLating valve, r. a piston provided at the outer end of the actuating rod, the piston dividing the cylinder into cylinder spaced on either the side of the piston, a port communicating with each space, so that, in response to governor demand fluid flowing out of one governor output enters one port into one cylinder space and displaces the piston within the cylinder, fluid being scavenged from the other cylinder space through the other port, movement of the piston actuating the metering activation means of the compensating air pressure regulating valve so as to change pilot pressure in an amount proportional to governor response. 